Visual field defect classification in the Zhongshan Ophthalmic Center-Brien Holden Vision Institute High Myopia Registry Study

Purpose To describe a new combined myopia and glaucoma visual field classification system in order to report the visual field defects in a population of mostly young Chinese high myopes aged 7-70 years. Methods A total of 1434 visual fields (including confirmatory repeats of abnormal defects) from 487 high myopes (sphere <=-6.0 D) were analysed from the prospective Zhongshan Ophthalmic Center-Brien Holden Vision Institute (ZOC-BHVI) High Myopia Registry Study. The predefined classification definitions covering high myopia and glaucoma categories were: normal, enlarged blind spot, abnormal suspect and abnormal with nine subtypes. Two independent graders reviewed the first 150 of 1434 fields for initial grading calibration and the remaining 1284 fields were used to assess intergrader agreement. For the percentage distribution of visual fields, the repeats and unreliable fields were excluded, leaving 894 fields. Results The intergrader agreement of this combined classification system was a. value of 0.61 (95% CI 0.59 to 0.63). Among the 894 unique fields, the most common visual field was normal at 33.7% followed by enlarged blind spot at 25.6%. The per cent of 'arcuate-like' field defects (combining nasal step, early arcuate and advanced arcuate) was 16.1% with advanced arcuate at 3.4%. Conclusions A proposed combined visual field classification for high myopia and glaucoma demonstrates acceptable intergrader agreement. A total of 16.1% of defects in young high myopes were found to mimic classic glaucomatous defects. These subjects are being followed prospectively to assess which ones will progress to differentiate myopic from glaucomatous field defects.